Electric vehicle

ABSTRACT

An electric vehicle without a propeller shaft including a rotating machine selectively functioning as an electric motor and a generator, configured to serve as a drive force source in the vehicle when the rotating machine functions as the electric motor, and functioning as the generator during running of the vehicle to thereby generate a regenerative brake force, and a wheel brake disposed on a wheel, used as a service brake, and generating a braking force corresponding to a brake request amount during running of the vehicle, the electric vehicle comprising: a third braking device disposed in a power transmission path between the rotating machine and a drive wheel to generate a braking force with a braking method other than regeneration during running of the vehicle.

This application claims priority from Japanese Patent Application No.2018-206893 filed on Nov. 1, 2018, the disclosure of which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an electric vehicle and, moreparticularly, to an electric vehicle causing a rotating machine disposedas a drive force source for running to function as a generator so as togenerate a regenerative brake force.

DESCRIPTION OF THE RELATED ART

There is known an electric vehicle, which does not include a propellershaft, having (a) a rotating machine selectively functioning as anelectric motor and a generator, configured to serve as a drive forcesource in the vehicle when the rotating machine functions as theelectric motor, and functioning as the generator during running of thevehicle to thereby generate a regenerative brake force, and (b) a wheelbrake disposed on a wheel, used as a service brake, and generating abraking force corresponding to a brake request amount during running ofthe vehicle. The vehicle described in Patent Document 1 is an examplethereof and includes a third braking device (braking force generatingmeans), such as an engine brake and an air resistance variable meanssuch as a rear wing including an angle adjustable flap, in addition to aregenerative brake using a rotating machine and a wheel brake.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-23568

SUMMARY OF THE INVENTION Technical Problem

However, for example, in an electric vehicle which does not include anengine in a power transmission path, engine brake cannot be obtained,and therefore, for example, when the regenerative brake using therotating machine cannot be used due to battery charge restriction, etc.,the wheel brake is frequently used and may cause a problem ofoverheating etc. It is conceivable that an air resistance variable meansor a road surface resistance variable means is used instead of theengine brake; however, this may be difficult to apply because of a largescale of equipment and a significant design change required for somevehicles. An electric vehicle including an engine in a powertransmission path has the same problem when the engine brake cannot beused for some reason.

The present invention was conceived in view of the situations and it istherefore an object of the present invention to provide an electricvehicle in which a third braking device can easily be disposed forsuppressing frequent use of a wheel brake when a regenerative brakeusing a rotating machine is unusable.

Solution to Problem

To achieve the above object, a first aspect of the present inventionprovides an electric vehicle without a propeller shaft including (a) arotating machine selectively functioning as an electric motor and agenerator, configured to serve as a drive force source in the vehiclewhen the rotating machine functions as the electric motor and configuredto generate a regenerative brake force when the rotating machinefunctions as the generator, and (b) a wheel brake disposed on a wheel,used as a service brake, and generating a braking force corresponding toa brake request amount during running of the vehicle, the electricvehicle comprising: (c) a third braking device disposed in a powertransmission path between the rotating machine and a drive wheel togenerate a braking force with a braking method other than regenerationduring running of the vehicle.

A second aspect of the present invention provides the electric vehiclerecited in the first aspect of the invention, wherein (a) the electricvehicle includes a speed reducing mechanism reducing a speed of rotationof an output shaft of the rotating machine and transmitting the rotationto a differential device, and wherein (b) the third braking device isdisposed on the output shaft and applies a braking force to the outputshaft.

A third aspect of the present invention provides the electric vehiclerecited in the first aspect of the invention, wherein (a) the electricvehicle comprises an electric drive unit including a differential devicedisposed parallel to an output shaft of the rotating machine, a speedreducing mechanism which reduces and transmits a rotation of the outputshaft to a speed reduction shaft and further reduces and transmits arotation of the speed reduction shaft to the differential device, and acasing housing the differential device and the speed reducing mechanismtogether with the rotating machine, and wherein (b) the third brakingdevice is disposed on the output shaft and applies a braking force tothe output shaft.

A fourth aspect of the present invention provides the electric vehiclerecited in the first aspect of the invention, wherein (a) the electricvehicle comprises an electric drive unit including a differential devicedisposed parallel to an output shaft of the rotating machine, a speedreducing mechanism which reduces and transmits a rotation of the outputshaft to a speed reduction shaft and further reduces and transmits arotation of the speed reduction shaft to the differential device, and acasing housing the differential device and the speed reducing mechanismtogether with the rotating machine, and wherein (b) the third brakingdevice is disposed on the speed reduction shaft and applies a brakingforce to the speed reduction shaft.

A fifth aspect of the present invention provides the electric vehiclerecited in any one of the first to fourth aspects of the invention,wherein the third braking device is an electromagnetic retardergenerating a braking force from an eddy current generated by anelectromagnetic induction action.

A sixth aspect of the present invention provides the electric vehiclerecited in any one of the first to fifth aspects of the invention,comprising a brake control device determining whether a regenerativecontrol of the rotating machine is available and controlling therotating machine and the third braking device such that the rotatingmachine generates the regenerative brake force when the regenerativecontrol is available and that the third braking device generates thebraking force when the regenerative control is unavailable.

Advantageous Effects of Invention

According to the electric vehicle as described above, the third brakingdevice is disposed in the power transmission path between the rotatingmachine and drive wheels to generate the braking force based on thebraking method other than regeneration, and therefore, even when theregenerative brake of the rotating machine is unusable due to batterycharge restriction etc., frequent use of the wheel brake can besuppressed by operating the third braking device. Since the thirdbraking device is disposed in the power transmission path between therotating machine and the drive wheels, the third braking device caneasily be disposed without requiring a significant design change ascompared to when an air resistance variable means or a road surfaceresistance variable means is disposed.

According to the electric vehicle recited in the second and thirdaspects of the invention, the rotation of the output shaft of therotating machine is reduced by the speed reducing mechanism andtransmitted to the differential device, and since the third brakingdevice is disposed on the output shaft of the rotating machine beforethe speed reduction, the braking torque of the third braking device maybe relatively small, so that the small-sized third braking device can becompactly disposed. The third aspect of the invention includes theelectric drive unit in which the speed reduction shaft of the speedreducing mechanism and the differential device are arranged parallel tothe output shaft of the rotating machine, and for example, the outputshaft of the rotating machine can be extended and projected from thecasing with the third braking device disposed on a projecting endportion of the output shaft or the third braking device can be disposedin the casing. Thus, the electric drive unit is more easily employed inthe electric vehicle than known electric drive units.

According to the fourth aspect of the invention, in the case that theelectric vehicle comprises the electric drive unit in which the speedreduction shaft of the speed reducing mechanism and the differentialdevice are arranged parallel to the output shaft of the rotatingmachine, since the third braking device is disposed on the speedreduction shaft, the rotation speed of the third braking device isreduced as compared to when the third braking device is disposed on theoutput shaft of the rotating machine as in the third aspect of theinvention, and the rotation balance is improved so that rotationvibration etc. are suppressed. The speed reduction shaft can be extendedand projected from the casing with the third braking device disposed ona projecting end portion of the speed reduction shaft or the thirdbraking device can be disposed in the casing. Thus, the electric driveunit is more easily employed in the electric vehicle than known electricdrive units, which is the same as the third aspect of the invention.

According to the electric vehicle recited in the fifth aspect of theinvention, since the electromagnetic retarder is disposed as the thirdbraking device, a fluid is not required as in the case of a fluid typeretarder or a hydraulic brake device, so that the electromagneticretarder can more easily be disposed.

According to the electric vehicle recited in the sixth aspect of theinvention, the availability of the regenerative control of the rotatingmachine is determined so that the rotating machine and the third brakingdevice are controlled such that the rotating machine generates theregenerative brake force if the regenerative control is available, andthat the third braking device generates the braking force if theregenerative control is unavailable, and therefore, if the regenerativecontrol of the rotating machine is unavailable due to charge restrictionof the battery etc., the third braking device is operated and thefrequent use of the wheel brake can appropriately be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic left side view of an electric vehicle of afront-mounted drive force source type that is an example of the presentinvention as viewed from the left side.

FIG. 2 is a diagram for explaining a schematic configuration of anelectric drive unit mounted on the electric vehicle of FIG. 1, includinga cross-sectional view taken along a vehicle width direction and showingmultiple axes developed and arranged in one plane and a diagram showinga main portion of a control system.

FIG. 3 is a flowchart for explaining an auxiliary brake control providedby a brake control device of FIG. 2.

FIG. 4 is a diagram for explaining another example of the presentinvention, corresponding to FIG. 2.

FIG. 5 is a diagram for explaining still another example of the presentinvention, corresponding to FIG. 2.

FIG. 6 is a diagram for explaining still another example of the presentinvention, corresponding to FIG. 2.

MODES FOR CARRYING OUT THE INVENTION

The present invention relates to an electric vehicle having a rotatingmachine selectively functioning as an electric motor and a generator andis suitably applied to an electric vehicle using only a rotating machinefor running; however, the present invention may be applied to a serieshybrid vehicle including an engine (internal combustion engine)dedicated to electric generation and a parallel hybrid vehicle in whichan engine is used as a drive force source, for example. The electricvehicle may use only a vehicle-mounted battery as an electric powersource for running or may be equipped with an electric power generatingdevice such as a fuel cell.

The present invention is suitably applied to a transversely-mountedelectric drive unit mounted on a vehicle in a posture in which an outputshaft of a rotating machine is disposed on a first axis and adifferential device is disposed on a second axis parallel to the firstaxis such that these axes are parallel to a vehicle width direction, andmay also be applied to a longitudinally-mounted electric drive unitmounted on the vehicle in a posture in which the output shaft of therotating machine is parallel to a vehicle longitudinal direction.Therefore, the posture of the output shaft of the rotating machine isnot particularly limited as long as the vehicle is an electric vehiclewithout a propeller shaft. A bevel gear type or planetary gear typedifferential gear device is suitable for the differential device;however, for example, if the vehicle is provided with a pair of clutchesconfigured to control a power transmission state in accordance with leftand right drive wheels, the pair of clutches can be regarded as thedifferential device. If the left and right drive wheels are rotationallydriven by respective different rotating machines, the differentialdevice is not necessary and, in that case, a third braking device may bedisposed in each of power transmission paths between the left and rightdrive wheels and the rotating machines.

A speed reducing mechanism or a speed increasing mechanism is disposedbetween the output shaft of the rotating machine and the differentialdevice as necessary. The speed reducing mechanism may be a speedreducing mechanism reducing speed at a constant speed reduction ratio,such as a parallel shaft type or a planetary gear type mechanism, forexample, or may be a step-variable transmission establishing a pluralityof gear positions different in speed change ratio with engagementdevices such as clutches and brakes, or a belt type continuouslyvariable transmission etc.

A wheel brake is mechanically coupled to a brake pedal stepped by adriver, for example, and is configured to mechanically generate abraking force corresponding to a stepping operation force thereof (brakerequest amount), or may have a braking force electrically controlled bya brake control device in accordance with the stepping operation forceetc. For example, during auto-cruise running in which the vehicleautomatically runs at a constant vehicle speed or automatically runswhile following a preceding vehicle, the braking force may electricallybe controlled by the brake control device in accordance with the brakerequest amount calculated for deceleration.

Although an electromagnetic retarder is suitably used for the thirdbraking device, various braking devices braking based on a brakingmethod other than regeneration can be employed such as a fluid typeretarder and a friction engagement type hydraulic brake device. In thecase of the electromagnetic retarder generating a braking force with anelectromagnet, the braking force can be increased or decreased bycontrolling an excitation current of the electromagnet. Theelectromagnetic retarder may generate a braking force by using apermanent magnet instead of the electromagnet or in addition to theelectromagnet. The third braking device is preferably a braking devicecapable of increasing and decreasing the braking force; however, abraking device unable to increase and decrease the braking force is alsousable.

EXAMPLE

An example of the present invention will now be described in detail withreference to the drawings. In the following example, the figures aresimplified or deformed as needed and portions are not necessarilyprecisely drawn in terms of dimension ratio, shape, etc.

First Example

FIG. 1 is a schematic left side view of an electric vehicle 8 that is anexample of the present invention as viewed from the left side. FIG. 2 isa diagram for explaining a schematic configuration of an electric driveunit 10 mounted on the electric vehicle 8, including a cross-sectionalview taken along a vehicle width direction and showing multiple axes (afirst axis S1 to a third axis S3) developed and arranged in one planeand a diagram showing a main portion of a control system. The electricdrive unit 10 includes a rotating machine 12 disposed on the first axisS1 and used as a drive force source, a transaxle 14 adjacently disposedon one end side of the rotating machine 12 side by side in a first axisS1 direction, and a casing 16 housing the rotating machine 12 and thetransaxle 14. The electric drive unit 10 is a transversely-mounted unitmounted on the electric vehicle 8 in such a posture that the first axisS1 is parallel to the vehicle width direction and is disposed in a frontportion of the electric vehicle 8 to rotationally drive front wheels 17f. Therefore, the electric vehicle 8 of this example is a front-wheeldrive vehicle of a front-mounted drive force source type in which theelectric drive unit 10 is disposed in the front portion of the vehicleto rotationally drive the front wheels 17 f for running. The electricdrive unit 10 of this example can be disposed in a rear portion of theelectric vehicle 8 to form a rear-wheel drive vehicle of a rear-mounteddrive force source type in which left and right rear wheels 17 r arerotationally driven for running.

The electric vehicle 8 is an electric vehicle including only a singlerotating machine 12 as a drive force source, and a predetermined highvoltage electric power is supplied from a battery 18 through a powercontrol unit (PCU) 19 such as an inverter to the rotating machine 12.The rotating machine 12 is a so-called motor generator selectivelyfunctioning as an electric motor and a generator and is subjected to aregenerative control during running of the vehicle 8 to function as agenerator, thereby generating a regenerative brake force. The battery 18may be mounted alone or may be provided with a power generator such as afuel cell as necessary and may be charged with electric power suppliedfrom the power generator as needed. For example, the power generator maybe a generator rotationally driven by an engine as in a series hybridvehicle.

The casing 16 includes a bottomed cylindrical gear casing portion 20, acylindrical first motor casing portion 22, and a bottomed cylindricalsecond motor casing portion 24. The first motor casing portion 22 isintegrally provided with a partition wall 22 a extending to the innercircumferential side, and one opening portion of the first motor casingportion 22 is integrally coupled to an opening portion of the gearcasing portion 20 by a bolt etc. so that a gear chamber 26 is formedbetween the gear casing portion 20 and the partition wall 22 a, and thetransaxle 14 is housed in the gear chamber 26. The transaxle 14corresponds to a power transmission mechanism transmitting an output ofthe rotating machine 12 to the front wheels 17 f.

An opening portion of the second motor casing 24 is integrally coupledto the other opening portion of the first motor casing 22 by bolts etc.,and a motor chamber 28 housing the rotating machine 12 is formed inside.The rotating machine 12 is a synchronous motor and includes a stator 30and a rotor 32 having an annular shape concentric with the first axisS1, and the rotor 32 has a diameter smaller than the stator 30 and isdisposed inside the stator 30 with an output shaft 34 disposed in acentral portion. The output shaft 34 is made up of multiple memberscoupled by splines etc. as necessary. The stator 30 is integrally fixedto the partition wall 22 a of the first motor casing portion 22 bymultiple bolts not shown, while the output shaft 34 is supportedrotatably around an axis coincident with the first axis S1 by the casing16 via multiple bearings. The first axis S1 corresponds to a rotatingmachine center line that is a center line of the rotating machine 12.

The transaxle 14 includes a differential device 50 disposed on thesecond axis S2 parallel to the first axis S1, and a gear type speedreducing mechanism 54 transmitting power between the output shaft 34 ofthe rotating machine 12 and a ring gear 52 of the differential device50. The gear type speed reducing mechanism 54 is a parallel shaft typegear mechanism reducing a speed of rotation of the output shaft 34 andtransmitting the rotation to the differential device 50 and includes areduction gear shaft 58 provided with a reduction large gear and areduction small gear. The reduction gear shaft 58 is disposed on thethird axis S3 parallel to the first axis S1 and the second axis S2 suchthat the speed of the rotation of the output shaft 34 is reduced andtransmitted and further reduces the speed of the rotation beforetransmission to the ring gear 52 of the differential device 50. Thedifferential device 50 is a bevel gear type differential mechanism andtransmits the power transmitted to the ring gear 52, from a pair of sidegears via a pair of left and right drive shafts 56 to the left and rightfront wheels 17 f. Therefore, the electric vehicle 8 of this example isan electric vehicle without a propeller shaft in which the power isdirectly transmitted from the gear type speed reducing mechanism 54 tothe differential device 50. The gear type speed reducing mechanism 54corresponds to a speed reducing mechanism, and the reduction gear shaft58 corresponds to a speed reduction shaft.

A wheel brake 60 used as a service brake is attached to each of thefront wheels 17 f and the rear wheels 17 r of the electric vehicle 8 asdescribed above. The wheel brake 60 is a hydraulic brake frictionallyengaged by hydraulic pressure and generates a braking forcecorresponding to a brake hydraulic pressure supplied from a wheel brakecontrol circuit 62 during running of the vehicle 8. The wheel brakecontrol circuit 62 is a hydraulic circuit having an electric oil pump, ahydraulic control valve, etc., and supplies the wheel brake 60 with thebrake hydraulic pressure for generating a predetermined braking forcecorresponding to a brake request amount when the hydraulic control valveetc. are controlled in accordance with a command signal supplied from abrake control device 64. The brake request amount is a steppingoperation force of a brake pedal (not shown) subjected to a steppingoperation by a driver, for example. The brake control device 64 is acontroller controlling the braking force of the vehicle 8 including thewheel brake 60, is configured to include a so-called microcomputer etc.,calculates the brake hydraulic pressure in accordance with the brakerequest amount based on a predetermined data map etc., and controls thehydraulic control valve etc. of the wheel brake control circuit 62 sothat the brake hydraulic pressure is output. The brake hydraulicpressure may mechanically be generated in accordance with the steppingoperation force of the brake pedal, and, in this case, the wheel brakecontrol circuit 62 controlling the brake hydraulic pressure and thecontrol of the brake hydraulic pressure by the brake control device 64can be eliminated.

The brake control device 64 also controls the power control unit 19 ofthe rotating machine 12 to provide a regenerative control so that therotating machine 12 functions as a generator during running of thevehicle and thereby generates a regenerative brake force. Specifically,to suppress frequent use of the wheel brake 60 on a downhill etc., theregenerative control of the rotating machine 12 is provided to generatethe regenerative brake force when the driver performs a manual operationfor requesting an auxiliary brake (corresponding to an engine brake ofan engine-drive vehicle) or when the necessity of the auxiliary brake isautomatically determined from a state of use of the wheel brake 60, roadinformation, etc. The magnitude of braking force of the auxiliary brakecan manually be set and changed by the driver or is automatically setand changed in accordance with a state of use of the wheel brake 60,road information, etc.

The electric vehicle 8 is provided with an electromagnetic retarder 70as a third braking device usable as the auxiliary brake in addition tothe wheel brake 60 and a regenerative brake through the regenerativecontrol of the rotating machine 12. The electromagnetic retarder 70generates a braking force from an eddy current generated by anelectromagnetic induction action and is attached to the output shaft 34.One end portion 34 a of the output shaft 34, i.e., the end portion onthe transaxle 14 side, or the end portion on the left side in FIG. 2, isextended to project from the gear casing portion 20 of the casing 16 tothe outside, and the electromagnetic retarder 70 is attached to the endportion 34 a. The electromagnetic retarder 70 includes a cylindricalrotating-side member 72 relatively non-rotatably coupled to the endportion 34 a via a rotation stopper such as splines and a cylindricalfixed-side member 74 disposed on the inner circumferential side of therotating-side member 72 and fixed to the gear casing portion 20, and themembers are both disposed concentrically with the first axis S1. Thefixed-side member 74 has a multiplicity of electromagnets 76 arranged ina circumferential direction of the fixed-side member 74 to face an innercircumferential surface of the rotating-side member 72 across a slightgap (clearance), and an excitation current of the electromagnets 76 iscontrolled by an electromagnetic retarder control circuit 78, so thatthe rotation of the rotating-side member 72 is braked with a brakingforce corresponding to the excitation current, and the rotation of theoutput shaft 34 and therefore the front wheel 17 f is accordinglybraked. The excitation current output from the electromagnetic retardercontrol circuit 78 is controlled in accordance with a command signalsupplied from the brake control device 64. An outer circumferentialsurface of the rotating-side member 72 is provided with a multiplicityof cooling fins 80 projecting to the outer circumferential side. In thisexample, the rotating-side member 72 and the electromagnets 76 aredisposed to face each other across the cylindrical gap around the firstaxis S1; however, the rotating-side member 72 and the electromagnets 76can be arranged side by side substantially parallel to each other in theaxial direction of the first axis S1 to face each other across adisk-shaped gap orthogonal to the first axis S1. Alternatively, theelectromagnets 76 can be disposed on the rotating-side member 72, andvarious other forms of electromagnetic retarders can be employed.

In the electric vehicle 8 as described above, the electromagneticretarder 70 can be used as the auxiliary brake for suppressing frequentuse of the wheel brake 60 on a downhill etc., in addition to theregenerative brake through the regenerative control of the rotatingmachine 12. The brake control device 64 provides an auxiliary brakecontrol in accordance with a flowchart of FIG. 3, for example, andthereby selectively uses the rotating machine 12 and the electromagneticretarder 70. At step ST1 of FIG. 3, it is determined whether anauxiliary brake request is made, and if an auxiliary brake request isnot made, the control is terminated, or if an auxiliary brake request ismade, step ST2 and subsequent steps are executed. The auxiliary brakerequest is made when the auxiliary brake is requested by a driver'smanual operation or when the necessity of the auxiliary brake isdetermined based on a state of use of the wheel brake 60, roadinformation, etc., and a magnitude of the braking force of the auxiliarybrake is determined at the same time.

At step ST2, it is determined whether the regenerative control of therotating machine 12 is available, based on whether a predefinedregenerative control provision permission condition is satisfied, forexample. The regenerative control provision permission condition is, forexample, that a remaining electric storage amount SOC of the battery 18is equal to or less than a predefined chargeable upper limit value, thata battery temperature is equal to or greater than a predefinedchargeable/dischargeable lower limit value, etc. Specifically, when theregenerative control of the rotating machine 12 is provided to generatethe regenerative brake force, the battery 18 must be charged withelectricity generated by the regenerative control, and therefore, if theremaining electric storage amount SOC exceeds the upper limit value, theregenerative control of the rotating machine 12 is unavailable. If thebattery temperature falls below the lower limit value and thecharge/discharge of the battery 18 is restricted, the regenerativecontrol of the rotating machine 12 is unavailable since the battery 18cannot be charged.

If the regenerative control of the rotating machine 12 is available,step ST3 is executed to use the rotating machine 12 as the auxiliarybrake, and the rotating machine 12 is subjected to the regenerativecontrol to generate a predetermined regenerative brake force. At stepST3, the electromagnetic retarder 70 can be used in addition to therotating machine 12 so that a predetermined braking force is generatedby using both. If the regenerative control of the rotating machine 12 isunavailable, step ST4 is executed to use the electromagnetic retarder 70as the auxiliary brake, and the electromagnets 76 of the electromagneticretarder 70 are excited to generate a predetermined braking force.

As described above, according to the electric vehicle 8 of this example,the electromagnetic retarder 70 is disposed as the third braking devicein a power transmission path between the rotating machine 12 and thefront wheels 17 f serving as drive wheels, and therefore, even when theregenerative brake of the rotating machine 12 is unusable due to chargerestriction of the battery 18 etc., the frequent use of the wheel brake60 can be suppressed by operating the electromagnetic retarder 70.

Since the electromagnetic retarder 70 is disposed in the powertransmission path between the rotating machine 12 and the front wheels17 f, the electromagnetic retarder 70 can easily be disposed withoutrequiring a significant design change as compared to when an airresistance variable means or a road surface resistance variable means isdisposed. The electric vehicle 8 of this example includes the electricdrive unit 10 in which the reduction gear shaft 58 of the gear typespeed reducing mechanism 54 and the differential device 50 are arrangedparallel to the output shaft 34 of the rotating machine 12, and theoutput shaft 34 is extended to project from the casing 16 to the outsidewith the electromagnetic retarder 70 attached to the end portion 34 a.Thus, the electric drive unit 10 is more easily employed in the electricvehicle 8 than known electric drive units.

The rotation of the output shaft 34 of the rotating machine 12 isreduced by the gear type speed reducing mechanism 54 and transmitted tothe differential device 50, and since the electromagnetic retarder 70 isdisposed on the output shaft 34 before the speed reduction, the brakingtorque of the electromagnetic retarder 70 may be relatively small, sothat the small-sized electromagnetic retarder 70 can be used andcompactly disposed.

Since the electromagnetic retarder 70 is disposed as the third brakingdevice, a fluid is not required as in the case of a fluid type retarderor a hydraulic brake device, so that the electromagnetic retarder 70 canmore easily be disposed.

The availability of the regenerative control of the rotating machine 12is determined so that the rotating machine 12 and the electromagneticretarder 70 are controlled so as to generate the regenerative brakeforce by using the rotating machine 12 as the auxiliary brake if theregenerative control is available, or to generate the braking force byusing the electromagnetic retarder 70 as the auxiliary brake if theregenerative control is unavailable, and therefore, if the regenerativecontrol of the rotating machine 12 is unavailable due to chargerestriction of the battery 18 etc., the electromagnetic retarder 70 isoperated and the frequent use of the wheel brake 60 can appropriately besuppressed.

Other examples of the present invention will be described. In thefollowing examples, portions substantially common to the examples aredenoted by the same reference numerals and will not be described indetail.

Second Example

An electric drive unit 100 of FIG. 4 is different from the electricdrive unit 10 of the first example in the arrangement position of theelectromagnetic retarder 70 serving as the third braking device.Specifically, the second example is the same in terms of the fact thatthe electromagnetic retarder 70 is attached to the output shaft 34 ofthe rotating machine 12; however, the other end portion 34 b of theoutput shaft 34, i.e., the end portion on the rotating machine 12 side,or the end portion on the right side in FIG. 4, is extended to projectfrom the second motor casing portion 24 of the casing 16 to the outside,and the electromagnetic retarder 70 is attached to the end portion 34 b.Even in the second example, the same effects as the first example can beobtained.

Third Example

An electric drive unit 110 of FIG. 5 is different from the electricdrive unit 10 of the first example in that a friction engagement typehydraulic brake device 112 is disposed as the third braking device.Specifically, a cover 114 housing the hydraulic brake device 112 isintegrally fixed to the gear casing portion 20 of the casing 16, and theoutput shaft 34 of the rotating machine 12 is disposed to project intothe cover 114 with the hydraulic brake device 112 disposed between theoutput shaft 34 and the cover 114. The hydraulic brake device 112 is amulti-plate brake, a single plate brake, a belt brake, etc., andgenerates a braking force corresponding to the brake hydraulic pressuresupplied from a brake control circuit 116. The brake control circuit 116is a hydraulic circuit having an electric oil pump, a hydraulic controlvalve, etc., similar to the wheel brake control circuit 62, and suppliesthe hydraulic brake device 112 with the brake hydraulic pressure forgenerating a predetermined braking force when the hydraulic controlvalve etc. are controlled in accordance with a command signal suppliedfrom the brake control device 64.

In this case, although it is necessary to dispose an oil passage to thehydraulic brake device 112 and to dispose an electric oil pumpgenerating a hydraulic pressure so that a structure is complicated ascompared to the electromagnetic retarder 70, the same effects as thefirst example can be obtained in terms of the fact that the frequent useof the wheel brake 60 can be suppressed by operating the hydraulic brakedevice 112 even when the regenerative brake of the rotating machine 12is unusable due to charge restriction of the battery 18 etc., that thehydraulic brake device 112 can easily be disposed as compared to when anair resistance variable means or a road surface resistance variablemeans is disposed, etc. Even in the electric drive unit 100 of FIG. 4,the hydraulic brake device 112 can be disposed instead of theelectromagnetic retarder 70.

Fourth Example

An electric drive unit 120 of FIG. 6 is different from the electricdrive unit 10 of the first example in the arrangement position of theelectromagnetic retarder 70 serving as the third braking device, and inthe fourth example, the electromagnetic retarder 70 is attached to thereduction gear shaft 58. Specifically, one end portion 58 a of thereduction gear shaft 58, i.e., the end portion on the side opposite tothe rotating machine 12, or the end portion on the left side in FIG. 6,is extended to project from the gear casing portion 20 of the casing 16to the outside, and the electromagnetic retarder 70 is attached to theend portion 58 a. The rotating-side member 72 of the electromagneticretarder 70 is relatively non-rotatably coupled to the end portion 58 aand the fixed-side member 74 is integrally fixed to the gear casingportion 20 as in the first example.

The same effects as the first example can be obtained also in this case,and since the electromagnetic retarder 70 is disposed on the reductiongear shaft 58, the rotation speed of the electromagnetic retarder 70 isreduced as compared to when the electromagnetic retarder 70 is disposedon the output shaft 34 of the rotating machine 12 as in the firstexample, and a rotation balance is improved so that rotation vibrationis suppressed. Therefore, this is suitably applied to an electricvehicle in which slight rotation vibrations cause a problem and anelectric vehicle in which rotation vibrations easily occur due to highrotation. As with the electric drive unit 110 of FIG. 5, the hydraulicbrake device 112 can be attached to the reduction gear shaft 58, insteadof the electromagnetic retarder 70.

Although the examples of the present invention have been described indetail with reference to the drawings, these are merely an embodiment,and the present invention can be implemented in variously modified andimproved forms based on the knowledge of those skilled in the art.

REFERENCE SIGNS LIST

8: electric vehicle (electric vehicle) 10, 100, 110, 120: electric driveunit 12: rotating machine 16: casing 17 f: front wheels (wheel, drivewheels) 17 r: rear wheels (wheel) 34: output shaft 50: differentialdevice 54: gear type speed reducing mechanism (speed reducing mechanism)58: reduction gear shaft (speed reduction shaft) 60: wheel brake 64:brake control device 70: electromagnetic retarder (third braking device)112: hydraulic brake device (third braking device)

What is claimed is:
 1. An electric vehicle comprising: a rotatingmachine selectively functioning as an electric motor and a generator,configured to serve as a drive force source in the vehicle when therotating machine functions as the electric motor, and configured togenerate a regenerative brake force when the rotating machine functionsas the generator; a wheel brake disposed on a drive wheel, used as aservice brake, and generating a braking force corresponding to a brakerequest amount during running of the vehicle; an electromagneticretarder disposed in a power transmission path between the rotatingmachine and the drive wheel to generate a braking force from an eddycurrent generated by an electromagnetic induction action during runningof the vehicle; and an electric drive unit including a differentialdevice disposed parallel to an output shaft of the rotating machine andtransmitting power to the drive wheel, a speed reducing mechanism whichreduces and transmits a rotation of the output shaft to the differentialdevice, and a casing housing the differential device and the speedreducing mechanism together with the rotating machine, wherein theelectric drive unit is a transversely-mounted electric drive unitmounted on the vehicle in a posture in which the output shaft and thedifferential device are parallel to a vehicle width direction, the powertransmission path includes a projecting portion which is extended toproject from the casing to outside, and the electromagnetic retardergenerates the braking force between the projecting portion and thecasing.
 2. The electric vehicle according to claim 1, wherein theprojecting portion is provided as one end portion of the output shaft,and the electromagnetic retarder is provided between the projectingportion of the output shaft and the casing and applies the braking forceto the output shaft.
 3. The electric vehicle according to claim 1,wherein the speed reducing mechanism includes a speed reduction shaftwhich is disposed parallel to the output shaft and which a rotation ofthe output shaft is reduced and transmitted to, and the speed reducingmechanism further reduces and transmits a rotation of the speedreduction shaft to the differential device, the projecting portion isprovided as one end portion of the speed reduction shaft, and theelectromagnetic retarder is provided between the projecting portion ofthe speed reduction shaft and the casing and applies the braking forceto the speed reduction shaft.
 4. The electric vehicle according to claim1, comprising a brake control device determining whether a regenerativecontrol of the rotating machine is available and controlling therotating machine and the electromagnetic retarder such that the rotatingmachine generates the regenerative brake force when the regenerativecontrol is available and that the electromagnetic retarder generates thebraking force when the regenerative control is unavailable.
 5. Theelectric vehicle according to claim 2, comprising a brake control devicedetermining whether a regenerative control of the rotating machine isavailable and controlling the rotating machine and the electromagneticretarder such that the rotating machine generates the regenerative brakeforce when the regenerative control is available and that theelectromagnetic retarder generates the braking force when theregenerative control is unavailable.
 6. The electric vehicle accordingto claim 3, comprising a brake control device determining whether aregenerative control of the rotating machine is available andcontrolling the rotating machine and the electromagnetic retarder suchthat the rotating machine generates the regenerative brake force whenthe regenerative control is available and that the electromagneticretarder generates the braking force when the regenerative control isunavailable.
 7. The electric vehicle according to claim 1, wherein theelectromagnetic retarder includes a cylindrical rotating-side memberrelatively non-rotatably coupled to the projecting portion, and acylindrical fixed-side member disposed on the inner circumferential sideof the rotating-side member and fixed to the casing, a rotation of therotating-side member is braked due to the electromagnetic inductionaction, and an outer circumferential surface of the rotating-side memberis provided with a multiplicity of cooling fins projecting to an outercircumferential side of the rotating-side member.